Modern integrated circuits are made up of transistors, capacitors, and other devices that are formed on semiconductor substrates. On a substrate, these devices are initially isolated from one another but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnects, such as vias and contacts. The quality of the interconnect structure affects the performance and the reliability of the fabricated circuit. Interconnections are increasingly determining the limits of performance and density of modern integrated circuits.
The interconnect structures may include tungsten plugs and aluminum lines. In newer generations of the integrated circuits, dual damascene structures, which include copper lines and vias formed using dual damascene processes, were also used to form the interconnect structures.